DESORPTION RATES OF 2 PCB CONGENERS FROM SUSPENDED SEDIMENTS - II - MODEL SIMULATION

A two-compartment diffusion model has been developed and applied to si mulate the desorption kinetics of two PCB congeners [2,5,2',5'-tetrach lorobiphenyl (PCB-52) and 2,4,5,2',4',5'-hexachlorobiphenyl (PCB-153)] from suspended aquatic sediments (experimental results presented in t he preceding paper). Simulation results suggest that (1) both non-equi librium sorption and non-uniform particle size distribution of the nat ural sediments used in this study may have contributed to the observed two-distinct-rate desorption behavior of PCBs; and (2) that the two-c ompartment diffusion model, which assumes that one fraction of PCBs in solid phase reaches an instantaneous equilibrium with the surrounding aqueous phase while the other fraction follows intraparticle diffusio n, fits the data far better than the single retarded pore diffusion mo del. Simulation results further suggest that increasing adsorption equ ilibration time (aging) will generally decrease the instantaneous equi librium fraction and the effective pore diffusion coefficient. (C) 199 8 Elsevier Science Ltd. All rights reserved.